Lighting device for dielectric barrier discharge lamp

ABSTRACT

This invention aims to decrease the leakage current of a dielectric barrier discharge lamp, and to prevent generation of the luminance slope between both electrodes. Electrodes  3  and  4  are formed in the outer surface of the dielectric barrier discharge lamp  1 , and the high voltage side of the high frequency power sources  5  and  6  is connected to the electrodes  3  and  4 , respectively. The low voltage side of the high frequency power sources  5  and  6  is connected to the grounding voltage GND. The output voltage waveform of the high frequency power sources  5  and  6  have different phases each other and inverted polarities each other.

FIELD OF INVENTION

[0001] The present invention relates to a lighting device for dielectricbarrier discharge lamp a kind of a discharge lamp, in which a phosphoris excited by an ultraviolet ray radiated by a dielectric barrierdischarge of a discharge gas enclosed in a discharge vessel resulting ina radiation of visible light.

BACKGROUND TECHNOLOGY

[0002] Fluorescent lamps are used as a light source for reading a copyin information equipments such as facsimile, copying machine, imagereader, and a display light source for a large size color displaydevice, electronic sign board. As a conventional fluorescent lamp usedfor such applications, a so-called inner electrode type fluorescent lampis known, having a lamp bulb in which a pair of electrodes are providedon both ends and a discharge medium such as rare gas etc. is enclosed.However, this kind fluorescent lamp has such drawbacks that theluminance distribution along the axis of the bulb is not uniform, thatthe end portions of the bulb turn black resulting in the decrease ofeffective light emitting length, and that the life is short. On theother hand, a so-called external electrode type dielectric barrierdischarge lamp having a lamp bulb, in which a pair of externalelectrodes are provided on both ends is also used for the abovementioned applications. This kind of fluorescent lamp has a more uniformluminance distribution along the bulb axis by containing mercury gasthan the inner electrode type fluorescent lamp, and has advantages thatthe bulb ends do not turn black, and the life is rather long.

[0003] Such dielectric barrier discharge lamp is operated by a lightingdevice shown in FIG. 1. A dielectric barrier discharge lamp 1 has such astructure that a phosphor film is formed on the inner surface of adielectric tubular glass bulb 2 and rare gas such as neon or argon etc.and metal vapor such as mercury etc. are enclosed inside the glass bulb.Also, electrodes 3 and 4 are provided on outer surface of the both endsof the tubular glass bulb 2. These electrodes 3 and 4 are formed bywinding a conductor composed of for example aluminum (Al) etc. along thecircumference direction of the bulb. A high frequency power source 5 isconnected between the pair of electrodes 3 and 4, with one electrode 4being connected with the ground potential GND.

[0004] When a voltage is applied between the electrodes 3 and 4 by thepower source 5, a high frequency electromagnetic field is generatedbetween the electrodes through an electrostatic capacity between theelectrodes. With the high frequency electromagnetic field, metal vaporsuch as mercury enclosed in the glass bulb 2 is excited to radiate theultraviolet ray. This ultraviolet ray excites the phosphor deposited onan inner surface of the glass bulb 2 to generate a visible light, whichis radiated out of the glass bulb 2.

[0005] The lighting method of the discharge lamp shown in FIG. 1 iscalled one side high voltage lighting method, because a high voltage offor example 2000 to 3000 V is applied on only one side of the pair ofelectrodes 3 and 4. With the configuration, a high voltage potentialdifference V is generated between the electrodes on both ends of thelamp, which is descended linearly from high voltage at the electrode 3 Vto the ground potential GND at the electrode 4 as shown in FIG. 2. Suchhigh potential difference between both ends of the lamp generates aleakage current. This leakage current is a phenomenon that a currentflowing through the tubular glass bulb 2 from one electrode 3 to anotherelectrode 4 leaks to the ground potential GND in the midway and theleakage current increases as the potential difference increases. Forthis reason, when a lamp is lighted by the lighting method shown in FIG.1 and FIG. 2, the current flowing through the tubular glass bulb 2 showscurrent difference between the high voltage side and the GND side. Thus,according to the one side high voltage lighting method, a so-calledluminances lope occurs in which the luminance of the lamp decreases fromthe high voltage end to the GND end of the tubular glass bulb.

[0006] Besides, there was a problem in conventional one side highvoltage lighting method, that ozone is produced around the high voltageelectrodes because such a high voltage for example as 2000 to 3000 V isapplied to the electrode 3.

[0007] Further, in conventional one side high voltage lighting method,because the potential difference between both electrodes is great, it isconfirmed that the temperature difference around the electrodes occurgiving a bad effect upon the lamp action.

[0008] Therefore, it is an object of the present invention to eliminatethe problems mentioned above, to prevent the luminance slope due to theleakage current based on the high voltage drive, and to supply alighting device for dielectric barrier discharge lamp capable ofobtaining almost uniform and sufficient luminance along the tube axis ofthe lamp bulb.

DISCLOSURE OF THE INVENTION

[0009] The lighting device for a dielectric barrier discharge lampaccording to the present invention includes, a dielectric barrierdischarge lamp composed of a lamp bulb inside which a discharge gas isenclosed and a pair of electrodes are provided on the outer surface ofboth ends, a first and a second high frequency voltage sources connectedbetween a ground potential and each of the pair of electrodes of thedischarge lamp, the first and the second high frequency voltage sourcessupplying to the pair of electrodes with a first and a second highfrequency voltages having different phases with each other.

[0010] Further, in the lighting device for a dielectric barrierdischarge lamp according to the present invention, the first and thesecond high frequency voltages are the sine wave voltages of the samefrequency.

[0011] Further, in the lighting device for a dielectric barrierdischarge lamp according to the present invention, the first and thesecond high frequency voltages have the same periods, differentpolarities and the same amplitudes with each other.

[0012] Further, in the lighting device for a dielectric barrierdischarge lamp according to the present invention, an inverter circuitis included, which includes a switching circuit which is supplied with aDC voltage by the DC source, an inverter transformer having a primarycoil which is supplied with an output of the switching circuit, and asecondary coil the center tap of which is connected with the groundpotential and a tertiary coil which generates feedback signal to theinput side of the switching circuit, wherein the first and the secondhigh frequency voltages which are generated by the secondary coil of theinverter transformer which has a grounded center tap, and coils on theboth sides are supplied with AC voltages having inverted phases witheach other.

[0013] Further, in the lighting device for a dielectric barrierdischarge lamp according to the present invention, the dielectricbarrier discharge lamps are composed of a plurality of dielectricbarrier discharge lamps connected in parallel or connected in serieswith each other.

[0014] Further, in the lighting device for a dielectric barrierdischarge lamp according to the present invention, the plurality ofdielectric discharge lamps are arranged nearly parallel with each other,the both ends of them are supported by being inserted into a pair ofelectrodes formed by electric conductive silicone rubber which arearranged by extending accross the bulb axis direction of the dielectricdischarge lamps, the pair of electrodes formed by electric conductivesilicone rubber are connected with the output ends of secondary coil ofthe inverter transformer.

[0015] Further, the lighting device for a dielectric barrier dischargelamp according to the present invention includes a transistor switchingcircuit which is supplied with a DC voltage is supplied, and a 1-input2-output inverter transformer having a primary coil which is suppliedwith an output of the switching circuit, and a secondary coil a centertap of which is connected with the ground potential and a tertiary coilwhich generates a feedback signal to an input side of the switchingcircuit, wherein on the output ends of the coils arranged on the bothsides of the center tap of the inverter transformer. AC voltages havinginverted phases with each other are generated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 shows a general construction of a conventional lightingdevice for a dielectric barrier discharge lamp.

[0017]FIG. 2 is a graph showing a relation between an electrode toelectrode distance and a voltage for explaining an operation of theconventional lighting device for a dielectric barrier discharge lamp.

[0018]FIG. 3 shows a general construction of a lighting device for adielectric barrier discharge lamp according to the present invention.

[0019]FIG. 4 shows a waveform of an output voltage of a high frequencysource in the dielectric barrier discharge lamp according to the presentinvention.

[0020]FIG. 5 is a graph showing the relation between electrode toelectrode distance and a voltage for explaining an operation of thelighting device for dielectric barrier discharge lamp according to thepresent invention.

[0021]FIG. 6 shows a waveform of the output voltage of the highfrequency source according to another embodiment of the presentinvention.

[0022]FIG. 7 shows waveforms of the output voltage of the high frequencysource showing the relation between electrode to electrode distance andvoltage to explain the operation of the lighting device for dielectricbarrier discharge lamp according to the further different embodiment ofthe present invention.

[0023]FIG. 8 shows waveforms of an output voltage of the high frequencysource showing the relation between electrode to electrode distance andvoltage to explain the operation of the lighting device for dielectricbarrier discharge lamp according to the further different embodiment ofthe present invention.

[0024]FIG. 9 shows waveforms of an output voltage of the high frequencysource according to the further different embodiment present invention.

[0025]FIG. 10 shows waveforms of the output voltage of the highfrequency source according to the further different embodiment thepresent invention.

[0026]FIG. 11 is a circuit diagram showing a lighting device for adielectric barrier discharge lamp according to the further differentembodiment of the present invention.

[0027]FIG. 12 is a circuit diagram showing a lighting device for adielectric barrier discharge lamp according to the further differentembodiment of the present invention.

[0028]FIG. 13 is a circuit diagram showing a lighting device for adielectric barrier discharge lamp according to the further differentembodiment of the present invention.

[0029]FIG. 14 is a circuit diagram showing a lighting device for adielectric barrier discharge lamp according to the further differentembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0030] The embodiments of the present invention will be explained belowreferring to the figures. FIG. 3 is a general circuit diagram of alighting device for a dielectric barrier discharge lamp, FIG. 4 is awaveform diagram of an output voltage of a high frequency source. First,in FIG. 3, a dielectric barrier discharge lamp 1 has a structure inwhich a phosphor film is formed on the inner surface of a straighttubular glass bulb 2. Electrodes 3 and 4 are provided on the both endsof outside the glass bulb 2. Rare gas is enclosed in the discharge spaceinside the glass bulb 2. As an enclosed gas, a single gas or a mixed gasis used which is selected from the rare gas such as, for example, neon,argon, helium, krypton, xenon etc. The electrodes 3 and 4 are formedwith an aluminum tape having a designated width wound at designatedpositions of the both ends of the glass bulb 2 along the circumferencedirection. Inside the glass bulb 2, a layer made of such material, asfor example, SiO₂, TiO₂, Ag, having a high reflection characteristics,may be provided. A transparent insulator film coating (not illustrated)composed of silicone resin or PET resin etc. is provided on the outersurface of the electrodes 3 and 4 to prevent a short circuit accidentbetween the electrode 3 and 4. Here, a metal tape such as silver tape ora conducting paint such as silver paste other than aluminum tape, may beused as the electrodes 3 and 4.

[0031] The first high frequency power source 5 is connected between oneelectrode 3 and the GND and the second high frequency power source 6 isconnected between the other electrode 4 and the GND.

[0032] Next, the operation of the embodiment of the present inventionthus arranged will be explained below.

[0033] In the dielectric barrier discharge lamp 1 the glass bulb 2serves as a dielectric substance as well, and thus discharge isperformed through the glass that is a dielectric substance. When highfrequency AC voltages are supplied from the first and the second highfrequency source 5 and 6 to each electrodes 3 and 4, the current doesnot flow directly from the electrodes 3 and 4 into the discharge spacein the glass bulb 2, but the current flows through the dielectricsubstance made of the glass, which lies between the discharge space andthe electrodes 3 and 4 and acts as a capacitor. That is, on an innersurface of the glass bulb 2, electric charge having equal quantity andopposite sign to that of on an outer surface of the glass bulb 2 facingthe electrodes 3 and 4 is induced by the polarization of the glass anddischarge occurs between the outer and the inner surface of the glassbulb through the discharge space. The charges induced on the inner faceof the glass bulb 2 are neutralized by the charges moved by thedischarge, decreasing the electric field in the discharge space, so thedischarge current stops to flow even if the voltage is appliedcontinuously to the electrodes 3 and 4. However, if the applied voltageincreases further, the discharge current continues. If the dischargeends after once discharge occurred, the discharge does not resume untilthe polarity of the applied voltage is reversed. That is, the currentflows only right after the polarity of the applied voltage is reversedand the discharge occurs. Other than the time, the current stops to flowwhile the charges are the accumulated on the surface of the glass bulb2. Because rare gas such as neon or argon is enclosed inside the bulb 2,atoms constituting the rare gas are excited to a resonant level bycollision with electrons during the discharge described, the excitedatoms in resonant level collide with atoms of rare gas in other baselevel to form an excimer of 2-atom molecule due to a high pressure ofthe rare gas. This excimer radiates ultraviolet ray and returns to tworare gas atoms at base level. The ultraviolet ray radiated by excimer isconverted into visible light by a phosphor and emits high luminancelight, since it does not exhibit self-absorption which is ordinary inresonant ultraviolet ray of atoms.

[0034]FIG. 4(A), (B) show output voltage waveforms of the first and thesecond high frequency power sources 5 and 6 respectively. As shown inthe figures, these output voltage waveforms have the same amplitude andhave phases different by 180° from each other. Assuming the amplitudesof the output voltages, the peak values, are V/2, +V/2 is applied on theelectrode 3 and −V/2 is applied on the electrode 4 at the time t2 whenthese waveforms become the peak value. As a result, as shown in FIG. 5,the potential difference between the electrode 3 and 4 becomes V whichis a necessary high voltage, while a ½ voltage of the peak voltage V isapplied on each of the electrode 3 and the electrode 4, to make thepotential at the center of the glass bulb 2 to be 0, that is, the GNDlevel. Also in FIG. 4, at the time t1 when the output voltage waveformof the first and the second high frequency source 5 and 6 becomes 0potential, the potentials of the electrode 3 and 4 become 0 and thepotential difference between the two electrodes also becomes 0. Further,at the time t4 when the output voltage wave form of the first and thesecond high frequency power source 5 and 6 becomes another peak value,−V/2 is applied on the electrode 3 and +V/2 is applied on the electrode4. As a result, the potential difference between the electrode 3 and 4becomes V which is a necessary high voltage. In this way, in a both sidehigh voltage lighting method of the present invention, the potentialdifference between the electrode 3 and 4 varies like a sine wave voltagewhich alternates with an amplitude V and with the same frequency as thatof the output voltage waveform of the first and the second highfrequency power source 5 and 6. However, the voltage applied on each ofthe electrode 3 and 4 is a sine wave voltage with an amplitude of V/2.

[0035] For this reason, the applied potential on the electrode 3 and 4becomes ½ of necessary lighting voltage when compared with theconventional one side high voltage lighting method, and thus the leakagecurrent is decreased to less than half. Therefore, the luminance slopebetween the electrode 3 and 4 along the glass bulb 2 hardly exists, anda luminance distribution of nearly uniform can be obtained.

[0036] Concerning the embodiment described above, a more specificexample will be explained. A dielectric barrier discharge lamp wasprepared by providing a 3-wavelength phosphor film of 20 mm thick on theinner surface of the straight tubular glass bulb 2 with the innerdiameter of 2.0 mm, the outer diameter of 2.6 mm, and the length of 350mm composed of borosilicate glass. On the outer surface of the glassbulb 2, an aluminum tape of 0.1 mm thick and 20 mm wide is arrangedwound along the circumference direction to form the electrodes 2 and 3.As an enclosure gas, a mixed gas having a composition of neon/argon=90mol %/10 mol % with enclosing pressure of 60 Torr, was used and 3 mgmercury was mixed. A high frequency power source 5 and 6 were used, eachhaving 2500 Vrms voltage and 45 KHz frequency and generating sine waveoutput voltages having 180° different phases by 180° from each other.When the output voltages of these high frequency power source 5 and 6were applied on the electrodes 3 and 4 respectively and a current of 10mA flowed through the dielectric barrier discharge lamp 1 lighting. Forcomparison, a lighting device according to the conventional single sidehigh voltage lighting method shown in FIG. 1 was used, where a sine waveoutput voltage having 2500 Vrms voltage and 45 KHz frequency was appliedon the electrodes 3 and 4 from the power source 5. The lamp current was5 mA. In the dielectric barrier discharge lamp according to the presentinvention compared with the conventional dielectric barrier dischargelamp, a high luminance light emission can be obtained having a twice aslarge discharge current as conventional one using a power sourceproviding the same output voltage as that of the conventional one. Theluminance slope found in conventional dielectric barrier discharge lampwas not found at all. This fact indicates that, the dielectric barrierdischarge lamp according to the present invention can reduce the outputvoltage of the high frequency source 5 and 6 to a half, that is, 1225Vrms, to be operated using the same discharge current as of theconventional dielectric discharge lamp. Thus, it is able to prevent theluminance slopeby reducing the leakage current.

[0037]FIG. 6 shows another voltage wave forms supplied from the firstand the second power sources 5 and 6. These waveforms have the samerepetition cycles T and are pulse voltage waveforms having oppositepolarities to each other. When these pulse voltages are-supplied to theelectrodes 3 and 4 respectively, the same effect as the sine wave sourceshown in FIG. 4 is obtained.

[0038]FIG. 7 shows yet other different voltage waveforms supplied fromthe first and the second sources 5 and 6. These waveforms have arectified half waveform of a sine wave instead of the pulse waveformshown in FIG. 6, and have the same phases but opposite polarities toeach other. When these half-wave voltages are supplied to the electrodes3 and 4, respectively, the same effect as in the sine wave voltage orpulse voltage shown in FIG. 4 or FIG. 6 is obtained. Each output voltagewaveforms of the first and the second sources 5 and 6 shown in FIG. 4,FIG. 6, and FIG. 7 have phases different by 180° or 0° with each other,but this relation is not always necessary. That is, the waveforms shownin FIG. 8 have a phase difference lagging of 180° compared with those inFIG. 4 with each other. The more the phase lags from 180°, the higherthan V/2 the voltage supplied to the electrodes 3 and 4 becomes. It canbe, however, kept lower than the potential V which is supplied in oneside high voltage lighting method. The pulse waveforms shown in FIG. 9have a phase difference lagging from 0° compared with the waveforms inFIG. 6. However, if two pulse voltage waveforms have opposite polaritiesto each other in the same time period, the same effect as in thewaveform shown in FIG. 6 is obtained. The rectified half waveforms shownin FIG. 10 have a phase difference lagging from 0° compared with that ofFIG. 7. However, if two half-wave rectified voltage waveforms haveopposite polarities to each other in the same time period, the sameeffect as in the waveform shown in FIG. 7 is obtained.

[0039] Further, the two voltage waveforms shown in FIG. 4 and FIG. 6 toFIG. 10 do not need to have the same peak values. In this case, thevoltage supplied on the electrodes 3 and 4 become higher than V/2, butcan be kept lower than the potential V which is supplied by one sidehigh voltage lighting method.

[0040]FIG. 11 is a circuit diagram showing another embodiment of thelighting device for a dielectric barrier discharge lamp according to thepresent invention. This lighting device is composed of resonance typeRoyer inverter circuit utilizing self-excited oscillation. On the inputterminal 11, a DC voltage is supplied from a DC source (notillustrated). The DC voltage is supplied to the base electrode of thetransistor 14 composing the inverter circuit through inductance 12 andresistor 13 in series. The inductance 12 is composed of a choke coilwhich keeps the input current flowing into the inverter circuitconstant. The inverter circuit is provided with another transistor 15,the emitter electrode of which is connected with the GND potentialtogether with that of the transistor 14. The collector electrodes of thetransistors 14 and 15 are connected with the both ends of the primarycoil 17 of the inverter transformer composing the inverter circuitrespectively. In this case, the collector electrode of the transistor 14is connected with the positive side of the primary coil 17, while thecollector electrode of the transistor 15 is connected with the negativeside of the primary coil 17. One end of the secondary coil 18 of theinverter transformer is connected with the GND, the other end isconnected with the electrode 3 of the dielectric barrier discharge lamp1. The inverter transformer 16 is also provided with a tertiary coil 19.Both ends of this tertiary coil 19 are connected with the baseelectrodes of the transistors 14 and 15 respectively to feedback thevoltage produced in the tertiary coil 19 to the bases of the transistors14 and 15. Between the both ends of the primary coil 17 of the invertertransformer 16, a capacitor 20 is connected which composes an LCresonance circuit together with the inductor component of the invertertransformer. The DC voltage supplied from the input terminal 11 is alsosupplied to a center tap of the primary coil 17 of the invertertransformer 16 through the inductance 12.

[0041] The DC voltage supplied from the input terminal 11 is connectedwith a center tap of a primary coil 23 of a second inverter transformer22 through an inductance 21. One end of the positive side of the primarycoil 23 is connected with the collector electrode of the transistor 15.While, the one end of the negative side of the primary coil 23 isconnected with the collector electrode of the transistor 14. That is,the primary coil 17 of the first inverter transformer 16 and the primarycoil 23 of the second inverter transformer 22 are connected to haveopposite polarities to each other with respect to the collector outputvoltages of the transistors 14 and 15. Between the both ends of theprimary coil 23 of the second inverter transformer 22, a secondcapacitor 24 for resonance are connected, which composes an LC resonancecircuit together with the inductance component of the second invertertransformer 22. While one end of the secondary coil 25 of the secondinverter transformer 22 is connected with the GND, the other end isconnected with the other electrode 4 of the dielectric barrier dischargelamp 1.

[0042] Next, the operation of the lighting device for a dielectricdischarge lamp thus composed will be explained. When the DC voltage isapplied to the input terminal 11, a current flows in the primary coil 17of the first inverter transformer 16 through the inductor 12. At thesame time, the DC voltage applied on the input terminal 11 is applied tothe base of the transistor 14 through the resistor 13. This inputvoltage is amplified by the transistor 14 and the amplified outputcurrent is supplied to the primary coil 17 of the first invertertransformer 16. This output current resonates, in the resonance circuitcomposed of the reactance of the first inverter transformer 16 and theresonance capacitor 20, with the frequency determined by these L, Cvalue to induce a voltage between the terminals of the tertiary coil 19of the inverter transformer 16. The induced voltage is a voltagecorresponding to the turns ratio of the primary coil 17 and the tertiarycoil 19 of the inverter transformer 16. At this time, in the tertiarycoil 19 of the inverter transformer 16, a current flows in the samedirection as that of the primary coil 17 and this current is input inthe base electrodes of the transistor 14 and 15 originating aself-excited oscillation. As a result, these transistors 14 and 15 areturned ON alternately at the resonance frequency. The oscillationfrequency at this time is determined by the reactance of the primarycoil 17 and the tertiary coil 19 of the inverter transformer 16, thecapacitor 20 for resonance, and the reactance component fed back fromthe secondary coil of the inverter transformer 16. Also, the outputvoltage of the inverter circuit is raised with the turns ratio of theprimary coil 17 and the secondary coil 18 of the inverter transformer 16and an AC voltage having the resonant frequency is output. This ACvoltage is output between the secondary coil 18 of the first invertertransformer 16 and the secondary coil 25 of the second invertertransformer 22. Here, the AC voltage waveform being output from thesecondary coil 18 of the first inverter transformer 16 and the ACvoltage waveform being output from the secondary coil 25 of the secondinverter transformer 22 have the inverted phases with each other.Therefore, a voltage potential equals to the sum of each of these ACvoltage amplitudes, is supplied between a pair of electrodes 3 and 4 ofthe dielectric barrier discharge lamp 1. In other words, it is possibleto light a discharge lamp free from the luminance slope caused by aleakage current by using an inverter circuit generating a voltage equalto a half of the voltage necessary for the lighting the dielectricbarrier discharge lamp 1.

[0043]FIG. 12 is a circuit diagram showing other embodiment of thelighting device for a dielectric discharge lamp according to the presentinvention. The lighting device of the present embodiment is alsocomposed of a resonance type Royer inverter circuit utilizing aself-excited oscillation similar to the embodiment shown in FIG. 11. Inthe present embodiment, however, the second inverter transformer 22 inthe embodiment of FIG. 11 is omitted. Except for this point, bothembodiments have nearly same circuit composition. For this reason, inFIG. 12, explanation is omitted by assigning the same symbols to theparts corresponding to those in FIG. 11 and only the differing portionsare explained below.

[0044] The inverter transformer 31 is a so-called 1-input 2-outputtransformer, the second coil 32 of which has a center tap 33 connectedwith the GND. This secondary coil 32 is wound in such a way that theboth coils have opposite winding directions with each other in the bothsides of the center tap 33, and each of the coils has more turns thanthat of the primary coil 17 to raise the voltages. With thisconfiguration, two voltage waveforms having phases difference of 180°from each other and having raised voltages are obtained at the twooutput ends of the secondary coil 32.

[0045] These output voltages are applied on the both electrodes 3 and 4of the dielectric barrier discharge lamp 1, so that the discharge lamp 1can be driven for lighting at a higher voltage than any of the amplitudeof these voltages, in a similar manner with the case in FIG. 11. Here,the primary coil 17 and the tertiary coil 19 of the inverter transformer31 have the same composition as the inverter transformer 16 shown inFIG. 11.

[0046] By using the 1-input 2-output type transformer for the invertertransformer 31, the primary sides of the transformer 31 are commonlyused completely and stability is improved because the core volumeincreases, compared with the case of using two transformers shown inFIG. 11.

[0047]FIG. 13 is a circuit diagram showing other embodiment of thelighting device of a dielectric barrier discharge lamp according to thepresent invention. In the embodiment, a plurality of the dielectricbarrier discharge lamps 1 are driven in parallel by the lighting deviceshown in FIG. 12. On both ends of the plurality of dielectric dischargelamps 1 arranged in parallel, the electrodes 41 and 42 composed of apair of bar shape electric conductive silicone rubber are provided whichare arranged parallel to the direction perpendicular to the plurality ofthe dielectric barrier discharge lamps 1. The both ends of a pluralityof the dielectric barrier discharge lamps 1 are inserted into aplurality of holes formed in the electric conductive silicone rubberelectrodes 41 and 42. A pair of bar shape electrodes 41 and 42 areconnected with the both ends of the secondary coil 32 of the invertertransformer 31 at the opposite ends of 41 and 42.

[0048] The electrodes 41 and 42 contact firmly with the outer surface oflamp bulb forming the dielectric barrier discharge lamp 1 withelasticity of the electric conductive silicone rubber to form outerelectrodes for mutually connecting with the both ends of a plurality ofdielectric barrier discharge lamps 1. Thus, the plurality of dielectricbarrier discharge lamps 1 are connected with the secondary coil 32 ofthe inverter transformer 31 in parallel.

[0049] With the lighting device according to the embodiment of thepresent invention thus composed, the electrodes formed by aluminum tapewound around the outer surface of the lamp bulb can be omitted, whichhave been generally used in the conventional dielectric barrierdischarge lamps of this kind. Also with this device, a relay board, leadwire, or electric conductive metal fittings are not needed, which werenecessary in the past for the simultaneous driving of the plurality ofdielectric barrier discharge lamps of this kind, so that the arrangementof the electrode portion can be extremely simplified.

[0050] Since the pair of bar shape electrodes 41 and 42 are, connectedwith the both ends of the secondary coil 32 of the inverter transformer31 at their opposite ends, the potential difference owing to theresistance of electric conductive silicone rubber is cancelled. As aresult, substantially equal voltages are applied to the plurality ofdielectric barrier discharge lamps. For this reason, there is anadvantage that lamp currents do not vary from one discharge lamp toanother, so that all the discharge lamps can be lighted with nearlyuniform luminance.

[0051]FIG. 14 is a circuit diagram showing still other embodiment of thelighting device for a dielectric barrier discharge lamp according to thepresent invention. In the embodiment, two dielectric barrier dischargelamps 1-1 and 1-2 are driven, which are connected in series with eachother. On the one end of these discharge lamps 1-1 and 1-2, a commonelectrode 3 is provided and electrodes 4-1 and 4-2, which areindependent from each other, are provided on the other ends. Terminalson a high voltage side of the high frequency source 5 and 6 areconnected with the independent electrodes 4-1 and 4-2 respectively. Theterminal on a low voltage side of these high frequency source 5 and 6are connected with the GND in the same manner as in the embodiment shownin FIG. 3., Specifically, an inverter circuit shown in FIG. 11 and FIG.12 is used for these high frequency sources 5 and 6. An electricconductive silicone rubber electrode 41 or 42 shown in FIG. 13 can beused for a common electrode 3. Here, the electrodes 4-1 and 4-2 may beconstructed by the aluminum tape wound around the outer surface of thelamp bulb as are generally used for the conventional dielectric barrierdischarge lamp of this kind.

[0052] With the present invention, in which a required high voltageoutput is supplied to a dielectric barrier discharge lamp using a highfrequency source of low output voltage, a lighting device for adielectric barrier discharge lamp can be provided, which prevents theluminance slope caused by a leakage current in high voltage driving, andwhich provides a sufficient and nearly uniform luminance along the tubeaxis of the lamp bulb.

1. A lighting device for a dielectric barrier discharge lamp comprising:a dielectric barrier discharge lamp having a lamp bulb inside which adischarge gas is enclosed and a pair of electrodes are formed on outersurface of both ends of the lamp bulb, and a first and a second highfrequency voltage sources each of which is connected between one of theelectrodes and a ground potential, wherein the first and the second highfrequency voltage sources respectively supply the electrodes with afirst and a second high frequency voltages having different phases witheach other.
 2. The lighting device for a dielectric barrier dischargelamp according to claim 1, wherein the first and the second highfrequency voltages are sine wave voltages of the same frequency.
 3. Thelighting device for a dielectric barrier discharge lamp according toclaim 2, wherein the first and the second high frequency voltages havethe same periods, different polarities with each other, and the sameamplitudes.
 4. The lighting device for a dielectric barrier dischargelamp according to any one of claim 1 to claim 3, wherein the first andthe second high frequency voltage sources are composed of an invertercircuit having an input of a DC source.
 5. The lighting device for adielectric barrier discharge lamp according to claim 4, wherein theinverter circuit comprises: a switching circuit to which a DC voltage issupplied from the DC source, and an inverter transformer having aprimary coil to which an output of the switching circuit is supplied, asecondary coil a center tap of which is connected with the groundpotential, and a tertiary coil generating a feedback signal to an inputside of the switching circuit, wherein the first and the second highfrequency voltages are supplied from the secondary coil of the invertertransformer, which has a grounded center tap and coils on both side ofthe center tap generating AC voltages having inverted phases with eachother.
 6. The lighting device for a dielectric barrier discharge lampaccording to claim 5, wherein a phosphor film is formed on the innersurface of the lamp bulb.
 7. The lighting device for a dielectricbarrier discharge lamp according to claim 1, wherein the first and thesecond high frequency voltages output the pulse waveform voltages havingnearly same frequencies.
 8. The lighting device for a dielectric barrierdischarge lamp according to claim 7, wherein the first and the secondhigh frequency voltages have nearly same amplitudes and invertedpolarities with each other.
 9. The lighting device for a dielectricbarrier discharge lamp according to claim 5, wherein the dielectricbarrier discharge lamps are composed of a plurality of dielectricbarrier discharge lamps connected in parallel or in series with eachother.
 10. The lighting device for a dielectric barrier discharge lampaccording to claim 9, wherein the plurality of dielectric barrierdischarge lamps are arranged nearly parallel with each other, the bothends are supported by being inserted into the electrodes which arecomposed of a pair of electric conductive silicone rubber and arrangedby extending across the tube axis direction of the dielectric barrierdischarge lamps, the pair of electrodes composed of electricallyconductive silicone rubber are connected with the output ends of thesecondary coil of the inverter transformer respectively.
 11. Thelighting device for a dielectric barrier discharge lamp according toclaim 10, wherein the electrodes composed of a pair of electricallyconductive silicone rubber, which are arranged extending across tubeaxis direction of the dielectric barrier discharge lamps, are connectedwith the output ends of the secondary coil of the inverter transformerat the opposite ends in their extended direction.
 12. The lightingdevice for a dielectric barrier discharge lamp according to claim 11,wherein a phosphor film is provided on the inner surface of the lampbulb.
 13. A lighting device for a dielectric barrier discharge lampcomprising: a transistor switching circuit to which is supplied with aDC voltage, and a 1-input 2-output inverter transformer having a primarycoil to which is supplied with an output of the switching circuit, and asecondary coil a center tap of which is connected with the groundpotential and a tertiary coil which generates a feedback signal to aninput side of the switching circuit, wherein output ends of the coilsformed on both sides of the center tap of the inverter transformergenerate AC voltages having inverted phases with each other.
 14. Thelighting device for a dielectric barrier discharge lamp according toclaim 13, wherein on the output ends of the secondary coil of theinverter transformer, each of elongated electrodes composed of a pair ofelectrically conductive silicone rubber, which are arranged nearlyparallel, is connected, and wherein both ends of a plurality ofdielectric barrier discharge lamps arranged nearly parallel aresupported by being inserted in the pair of electrodes.
 15. The lightingdevice for a dielectric barrier discharge lamp according to claim 14,wherein the pair of electrodes composed of electrically conductivesilicone rubber are connected with the output ends of the secondary coilof the inverter transformer at the opposite ends in the longitudinaldirection.
 16. The lighting device for a dielectric barrier dischargelamp according to claim 15, wherein a phosphor film is provided on theinner surface of the lamp bulb.